This invention relates to a method of forming a refractory metal contact over a silicon substrate in a solid state structure, and to related structures. More particularly, the invention relates to a method employing a sacrificial silicon layer that serves as a nucleation layer for subsequent deposition of a refractory material to form a contact.
Conductive metal contacts are frequently found in semi-conductor devices, and typically are formed by deposition of a refractory material, such as tungsten or the like, confined by a silicon oxide layer previously deposited over a conducting substrate containing, for example, a silicide. Steps in the conventional method of forming such contacts, and the nature of a problem that sometimes arises, are best understood with reference to FIGS. 1, 2, 3 and 4(A)-(B) hereof.
FIG. 1 is a cross-sectional view of a relevant portion of the underlying structure, wherein an underlying silicide layer 100 serves as a substrate 4 with an oxide layer 102 formed thereon. The location, shape and size of the desired conductor is determined by a through opening 104 formed in the oxide layer 102, with exposed surface 106 of the silicide serving as a bottom 106 of the opening 104. As best seen in FIG. 2, a thin metallic layer 200 is then deposited at the bottom of aperture 104 to serve as a contact liner. Then, per FIG. 3, a thin nucleation layer 300 of a refractory material such as tungsten is formed in the presence of silane gas to cover oxide layer 102, the sides 108 of aperture 104, per liner 200. This is followed, per FIG. 4(A), by the deposition of a layer 400 containing the desired refractory material in an amount sufficient to totally cover and fill up the inside of aperture 104 and to extend over the upper surface of oxide layer 102. Note that the nucleation layer 300 becomes, in effect, absorbed within the refractory layer 400.
Unfortunately, when a refractory material such as tungsten is deposited from decomposition of WF6 through the use of either physical vapor deposition (PVD) or chemical vapor deposition (CVD), particularly during a chemical vapor deposition step, some of the fluorine released from decomposition of WF6 combines with silicon in the silicide layer 100 and a propensity to form an undesirable region 402, as is probably best seen in the enlarged view in FIG. 4(B).
An example of a prior patent which appears to address a similar problem is U.S. Pat. No. 5,804,499, to Dehm et al., titled “Prevention of Abnormal WSix Oxidation by In-Situ Amorphous Silicon Deposition”, which suggests a process in which amorphous silicon is deposited in a thin layer on top of tungsten silicide to prevent abnormal WSix oxidation during subsequent process steps. The layer of amorphous silicon as mentioned in this patent is bounded by a spacer also made of amorphous silicon. The reference does not teach the provision of a continuous layer of silicon to address the problem at issue.
The present invention seeks to address this particular problem in a simple and efficient manner.